This invention relates to a plastic package, in particular, a mostly plastic case designed to hold various objects, such as, for example, a video cassette.
Plastic packages such as video cases have been manufactured for many years. The typical process consists of thermo-vacuum-forming a relatively rigid thermoplastic sheet, such as polyvinyl chloride (PVC), to form opposed inner contoured surfaces configured to receive and hold the video cassette or other object when the case is closed by folding about its spine, then covering the back side of the rigid sheet with a cardboard stiffener, an opaque relatively flexible PVC sheet, and a clear relatively flexible PVC sheet, followed by heat-sealing together the sandwich so formed so as to seal the cardboard stiffener between the rigid PVC and the flexible opaque PVC sheets and the latter to each other and to the clear PVC sheet around three sides so that advertising material for the contents of the case can be inserted through the unsealed fourth side and thus be visible to prospective customers and users of the video cassette. Typically, for PVC, the relatively rigid sheet has a thickness between about 0.008 and 0.030 inches (in.), and the relatively flexible sheets have thicknesses ranging between about 0.003 and 0.020 in. The term "rigid" or "relatively rigid" is a term of art meaning a sheet thickness that will hold its shape when thermoformed, is usually but not always thicker than the flexible sheet or relatively flexible sheets, but still has sufficient flexibility to allow the case to bend easily around its spine and thus easily open and close. However, this degree of flexibility is insufficient to stiffen the case sides, which in use are not supposed to bend. Hence, it is common practice to insert a stiffener member in the case sides to stiffen the latter. Typically, the stiffener member is made of a non-heat-sealable material such as, for example, inexpensive cardboard about 0.018 to 0.120 in. thick, with score lines or slits defining a center spine to allow the flat sides of the stiffener member to bend around the score lines or slits when the case is closed.
The trend for many years has been to reduce the manufacturing cost of such cases. The major expense is labor, and a major way to reduce labor costs is to increase production. The production expenses include inserting advertising material in the cover, closing and opening the finished case, and at times opening up the case, inserting a conventional video cassette and closing the case. In some circumstances, especially when the advertising material is relatively thick, a normally closed case will spring open during manufacture, causing delays and interrupting the case assembly process. The typical closure for holding the case closed is an angled side at one case side adapted to mate in a friction fit with an angled side on the other case side. This closure has not proven entirely satisfactory especially as production rates increased, primarily because of the close tolerences required to be maintained for satisfactory operation.